Image pickup apparatuses are useful instruments for acquiring image information and applied to various fields such as portable appliances, in-vehicle equipment, medical instruments and equipment, and industrial instruments and equipment. A demand for more intelligent range imagery input apparatuses capable of acquiring not only two-dimensional image data, but also range information including a distance from a subject and a three-dimensional shape of the subject is also increasing. Such range imagery input apparatuses are actually used in various places. However, it is known that the lens shape of an image pickup apparatus varies and accordingly, the optical conditions of the apparatus change due to changes in the environmental conditions (especially, due to a temperature change) in which the image pickup apparatus is placed.
A known technique for correcting optical conditions fluctuating due to temperature changes is disclosed in Patent Document 1 listed below. An image pickup apparatus disclosed in this document comprises a lens unit consisting of multiple optical lens elements arranged in the same plane; an image pick-up device having multiple image pick-up regions, each region corresponding to one of the optical lens elements; and a temperature sensor positioned in contact with the lens unit to sense the temperature of the lens unit. Distances between the optical axes of the optical lens elements are corrected based upon the sensed temperature, and the range from the subject is calculated after the correction.
Patent Document 2 discloses an image pickup apparatus that includes a lens array with plural lenses arranged into a single unit; plural image-pickup regions, each region corresponding to one of the lenses of the lens array; and a housing that holds the lens array. The lens array is fixed to the housing at a predetermined point. The lens array is held at the housing so as to be deformable according to thermal expansion with respect to the predetermined point.
Patent Document 3 discloses an image correcting apparatus for correcting optically caused positional displacement of the captured image taken by a stereo camera. In this document, the positional displacement due to variation with time is corrected according to the detected position of a marker.
Patent Document 4 discloses a stereo camera system that extracts a feature quantity from an image and selects calibration data based upon the feature quantity.
However, it is generally known that variations in the environmental temperatures cause the lens shape of an image pickup apparatus to change, and that the optical conditions inevitably change. Especially when using a range determination device with a short baseline length, such as a system disclosed in the above-described Patent Document 2 employing a combination of an image pickup sensor and a lens array to carry out range measurement, the ratio of change in the baseline length due to a temperature change is great, and therefore the range determination result is significantly affected. To overcome this problem, Patent Document 2 proposes the structure for holding the lens array at a single point to preclude adverse influence of stresses in the adhesives or the shielding blocks varying among devices. However, this method requires a temperature to be sensed although not explicitly described. In addition, influence of the device variability cannot be completely removed.
Patent Documents 3 and 4 are directed to a method for correcting aging variation in a stereo camera system, focusing on a device for correcting an external parameter, that is, a distance between cameras, and these methods require multiple markers.    Patent Document 1: JP 2009-250785 A    Patent Document 2: JP 2009-53011 A    Patent Document 3: JP H11-325890 A    Patent Document 4: JP 2004-354257 A